Some properties of membrane-bound, solubilized and reconstituted into liposomes H+-ATPase of vacuoles of Saccharomyces carlsbergensis

A rapid method for the preparation of ultrapure, functional lysosomes using functionalized superparamagnetic iron oxide nanoparticles

Lysosomes are an emerging and increasingly important cellular organelle. With every passing year, more novel proteins and key cellular functions are associated with lysosomes. Despite this, the methodologies for their purification have largely remained unchanged since the days of their discovery. With little advancement in this area, it is no surprise that analysis of lysosomal function has been somewhat stymied, largely in part by the change in buoyant densities that occur under conditions where lysosomes accumulate macromolecules. Such phenotypes are often associated with the lysosomal storage diseases but are increasingly being observed under conditions where lysosomal proteins or, in some cases, cellular functions associated with lysosomal proteins are being manipulated. These altered lysosomes poise a problem to the classical methods to purify lysosomes that are reliant largely on their correct sedimentation by density gradient centrifugation. Building upon a technique developed by others to purify lysosomes magnetically, we have developed a unique assay using superparamagnetic iron oxide nanoparticles (SPIONs) to purify high yields of ultrapure functional lysosomes from multiple cell types including the lysosomal storage disorders. Here we describe this method in detail, including the rationale behind using SPIONs, the potential pitfalls that can be avoided and the potential functional assays these lysosomes can be used for. Finally we also summarize the other methodologies and the exact reasons why magnetic purification of lysosomes is now the method of choice for lysosomal researchers.

V-ATPase dysfunction suppresses polyphosphate synthesis in Saccharomyces cerevisiae

The yeast Saccharomyces cerevisiae accumulates the high levels of inorganic polyphosphates (polyPs) performing in the cells numerous functions, including phosphate and energy storage. The effects of vacuolar membrane ATPase (V-ATPase) dysfunction were studied on polyP accumulation under short-term cultivation in the Pi-excess media after Pi starvation. The addition of bafilomycin A1, a specific inhibitor of V-ATPase, to the medium with glucose resulted in strong inhibition of the synthesis of long-chain polyP and in substantial suppression of short-chain polyP. The addition of bafilomycin to the medium with ethanol resulted in decreased accumulation of high-molecular polyP, while the accumulation of low-molecular polyP was not affected. The levels of polyP synthesis in the mutant strain with a deletion in the vma2 gene encoding a V-ATPase subunit were significantly lower than in the parent strain in the media with glucose and with ethanol. The synthesis of the longest chain polyP was not observed in the mutant cells. The synthesis of only the low-polymer acid-soluble polyP fraction occurred in the cells of the mutant strain. However, the level of polyP1 was nearly tenfold lower than compared to the cells of the parent strain. Both bafilomycin A1 and the mutation in vacuolar ATPase subunit vma2 lead to a considerable decrease of cellular polyP accumulation. Thus, the defects in ΔμH(+) formation on the vacuolar membrane resulted in the decrease of polyP biosynthesis in S. cerevisiae.

Inorganic polyphosphates and exopolyphosphatases in cell compartments of the yeast Saccharomyces cerevisiae under inactivation of PPX1 and PPN1 genes

Purified fractions of cytosol, vacuoles, nuclei, and mitochondria of Saccharomyces cerevisiae possessed inorganic polyphosphates with chain lengths characteristic of each individual compartment. The most part (80-90%) of the total polyphosphate level was found in the cytosol fractions. Inactivation of a PPX1 gene encoding ~40-kDa exopolyphosphatase substantially decreased exopolyphosphatase activities only in the cytosol and soluble mitochondrial fraction, the compartments where PPX1 activity was localized. This inactivation slightly increased the levels of polyphosphates in the cytosol and vacuoles and had no effect on polyphosphate chain lengths in all compartments. Exopolyphosphatase activities in all yeast compartments under study critically depended on the PPN1 gene encoding an endopolyphosphatase. In the single PPN1 mutant, a considerable decrease of exopolyphosphatase activity was observed in all the compartments under study. Inactivation of PPN1 decreased the polyphosphate level in the cytosol 1.4-fold and increased it 2- and 2.5-fold in mitochondria and vacuoles, respectively. This inactivation was accompanied by polyphosphate chain elongation. In nuclei, this mutation had no effect on polyphosphate level and chain length as compared with the parent strain CRY. In the double mutant of PPX1 and PPN1, no exopolyphosphatase activity was detected in the cytosol, nuclei, and mitochondria and further elongation of polyphosphates was observed in all compartments.

Inorganic polyphosphate and exopolyphosphatase in the nuclei ofSaccharomyces cerevisiae: dependence on the growth phase and inactivation of thePPX1 andPPN1 genes

Nuclei of the yeast Saccharomyces cerevisiae possess inorganic polyphosphates (polyP) with chain lengths of ca. 10-200 phosphate residues. Subfractionation of the nuclei reveals that the most part of polyP is not associated with DNA. Transition of the yeast cells from stationary phase to active growth at orthophosphate (P(i)) excess in the medium is followed by the synthesis of the shortest polyP (<15 phosphate residues) and hydrolysis of the high-molecular polyP (>45 phosphate residues) in the nuclei. Nuclear exopolyphosphatase (exopolyPase) activity does not depend on the growth phase. The PPX1 gene encoding the major cytosolic exopolyPase does not encode the nuclear one and its inactivation has no effect on polyP metabolism in this compartment. Under inactivation of the PPN1 gene encoding another yeast exopolyPase, elimination of the nuclear exopolyPase is observed. The effect of PPN1 inactivation on the polyP level in the nuclei is insignificant in the stationary phase, while in the exponential phase this level increases 2.3-fold as compared with the parent strain of S. cerevisiae. In the active growth phase, no hydrolysis of high-molecular polyP is detected while the synthesis of short-chain polyP is retained. The data obtained indicate substantial changes in polyP metabolism in nuclei under the renewal of active growth, which only partially depends on the genes of polyP metabolism known to date.

Inactivation of endopolyphosphatase gene PPN1 results in inhibition of expression of exopolyphosphatase PPX1 and high-molecular-mass exopolyphosphatase not encoded by PPX1 in Saccharomyces cerevisiae

Saccharomyces cerevisiae possesses multiple forms of exopolyphosphatases, the enzymes involved in the metabolism of inorganic polyphosphates, which are important regulatory compounds. In S. cerevisiae, inactivation of endopolyphosphatase gene PPN1 leads to the inhibition of expression of both exopolyphosphatase PPX1 and high-molecular-mass exopolyphosphatase of approximately 1000 kDa not encoded by PPX1. In the single endopolyphosphatase mutant CRN, the expression of exopolyphosphatase PPX1 decreases 6.5-fold and 2.5-fold at the stationary and exponential growth phases, respectively, as compared with the parent strain CRY. In this mutant, the activity of the high-molecular-mass exopolyphosphatase of approximately 1000 kDa decreases approximately 10-fold as compared with that in strains with the PPN1 gene. In a double mutant of PPX1 and PPN1, no exopolyphosphatase activity is detected in the cytosol at the stationary growth phase. Thus, the exopolyPase activity in cell cytosol depends on the endopolyPase gene PPN1.

ATP leakage from yeast cells treated by extracellular glycolipids of Pseudozyma fusiformata

The ustilaginaceous yeast Pseudozyma fusiformata secreted glycolipids which were lethal to many yeasts and fungi more active at pH of about 4.0, and in the temperature range of 20-30 degrees C. Purified glycolipids enhanced non-specific permeability of the cytoplasmic membrane in sensitive cells, which resulted in ATP leakage and susceptibility of the cells to staining with bromocresol purple. Cells of Saccharomyces cerevisiae lost the ability to acidify the medium. Basidiomycetous yeasts were more sensitive to the glycolipids than ascomycetous ones. The minimal effective glycolipid concentration was 0.13 and 0.26 mg ml(-1) for Cryptococcus terreus and Filobasidiella neoformans, while for Candida albicans and Saccharomyces cerevisiae it was 1.0 and 1.6 mg ml(-1).

Effect of PPX1 inactivation on exopolyphosphatases of different cell compartments of the yeast Saccharomyces cerevisiae

Inactivation of PPX1 encoding a major exopolyphosphatase (PPX1) in Saccharomyces cerevisiae results in a change of exopolyphosphatase spectra in the yeast cells. In the PPX1-deficient strain, an elimination of approximately 45 kDa enzyme is observed in cytosol and cell envelopes, and the activity of an exopolyphosphatase with a molecular mass of approximately 830 kDa increases 5-fold in the cytosol. These two enzyme activities differ greatly from each other not only in molecular masses but also in biochemical properties. Inactivation of PPX1 does not result in any changes in the content and properties of vacuolar exopolyphosphatase as compared with the wild strain of S. cerevisiae. In response to PPX1 mutation, exopolyphosphatase properties in the cell as a whole undergo modifications including the ability to hydrolyze polyphosphates with different lengths of the chain.

Properties of the V-type ATPase from the excretory system of the usherhopper, Poekilocerus bufonius

The bafilomycin A(1) and N-ethylmaleimide (NEM)-sensitive (V-type) ATPase was partially purified from the apical membrane-rich fractions of excretory system (Malpighian tubules and hind gut) of P. bufonius. Enzymatic activity was inhibited by bafilomycin A(1) (IC(50) = 1.3 nM) and NEM (IC(50) = 10.1 microM). The V-type ATPase activity is confined to the apical membrane fraction, while the activity of Na(+)/K(+) -ATPase forms the major part of the basal membrane fraction. The optimal pH required for maximal activity of V-type ATPase was pH 7.5. The effect of 30 mM of various salts on ATPase activity was investigated. NaCl and KCl caused increases of 175% and 184%, respectively. Other chloride salts also caused an increase in activity in the following ascending order: RbCl, LiCI, choline Cl, NaCI, KCl and tris-HCl. The activity of V-type ATPase was stimulated by a variety of different anions and cations, and HCO(3)(-) was found to be the most potent cationic activator of ATPase activity. The present results show that the properties of V-type ATPase of P. bufonius are similar to those reported for other insect tissues.

The yeast mutant vps5Delta affected in the recycling of Golgi membrane proteins displays an enhanced vacuolar Mg2+/H+ exchange activity

Growth of the yeast vacuolar protein-sorting mutant vps5Delta affected in the endosome-to-Golgi retromer complex was more sensitive to Mg2+-limiting conditions than was the growth of the wild-type (WT) strain. This sensitivity was enhanced at acidic pH. The vps5Delta strain was also sensitive to Al3+, known to inhibit Mg2+ uptake in yeast cells. In contrast, it was found to be resistant to Ni2+ and Co2+, two cytotoxic analogs of Mg2+. Resistance to Ni2+ did not seem to result from the alteration of plasma-membrane transport properties because mutant and WT cells displayed similar Ni2+ uptake. After plasma-membrane permeabilization, intracellular Ni2+ uptake in vps5Delta cells was 3-fold higher than in WT cells, which is consistent with the implication of the vacuole in the observed phenotypes. In reconstituted vacuolar vesicles prepared from vps5Delta, the rates of H+ exchange with Ni2+, Co2+, and Mg2+ were increased (relative to WT) by 170%, 130%, and 50%, respectively. The rates of H+ exchange with Ca2+, Cd2+, and K+ were similar in both strains, as were alpha-mannosidase and H+-ATPase activities, and SDS/PAGE patterns of vacuolar proteins. Among 14 other vacuolar protein-sorting mutants tested, only the 8 mutants affected in the recycling of trans-Golgi network membrane proteins shared the same Ni2+ resistance phenotype as vps5Delta. It is proposed that a trans-Golgi network Mg2+/H+ exchanger, mislocalized to vps5Delta vacuole, could be responsible for the phenotypes observed in vivo and in vitro.

Characterization of ATPases of apical membrane fractions from Locusta migratoria Malpighian tubules

Apical and basal membrane fractions from Locusta Malpighian tubules were prepared and were characterized by marker enzyme analysis. The apical membranes contained an azide- and orthovanadate-insensitive ATPase activity that was inhibited by bafilomycin A1 (IC50 = 0.44 nM) and NEM (IC50 = 2.15 microM), and thus was characterized as putative V-type ATPase. The enzyme was stimulated by a variety of monovalent cations (Tris > K = Na > choline > Li = Rb) maximal stimulation occurring at 30-40 mM. It was also stimulated by a variety of monovalent anions (maximal activation 30-40 mM), but was strongly inhibited by nitrate and thiocyanate. SDS-PAGE separation of proteins present in the various membrane fractions was carried out. The apical membrane fraction alone contained a 28 kDa protein band that bound a monoclonal antibody specific for a 28 kDa peptide which was a component of the V-type ATPase from midgut of Manduca sexta and, in native gels, possessed ATPase activity which was also sensitive to both bafilomycin and NEM but not to azide or orthovanadate. Binding of the fluorescent monoclonal antibody was located at the apical boundary of the tubule cells. It was concluded that a V-type ATPase is present at the apical surface of Locusta Malpighian tubule cells and that it is involved in their secretory functioning.

Comparison of exopolyphosphatases of different yeast cell compartments

Purified cell-envelope polyphosphatase as well as polyphoshatase activities of cytosol and isolated vacuoles, of nuclei and mitochondria of the yeast Saccharomyces cerevisiae were compared. The polyphosphatases of cell envelope and cytosol are similar, the polyphosphatases of nuclei, vacuoles and mitochondria differ in their kinetic properties, substrate specificity, requirements in divalent cations and in some effector actions both from these and from each other.

Ca(2+)-transporting ATPase(s) of the reticulum type in intracellular membranes of Saccharomyces cerevisiae: biochemical identification

Several lines of evidence are presented to show that the Ca(2+)-ATPase activity of total yeast membranes is due to the reticulum (R) type of Ca(2+)-ATPase: (1) Neither calmodulin nor low concentrations of calmodulin antagonists change Ca2+ uptake; (2) removal of plasma membranes (PM) following Con A treatment of spheroplasts (SP) does not significantly alter Ca2+ uptake by the remaining membranes, but increases its specific activity 3.5-fold; (3) after incubation of membranes with [gamma-32P]ATP, SDS-PAGE shows the formation of acyl phosphate intermediates with molecular masses of around 100, 180-190 and 205 kDa; formation of these acyl phosphates requires Ca2+ and is blocked by cyclopiazonic acid, La3+ ions and in the absence of Ca2+. The data on fractionation of yeast membranes are consistent with the suggestion that both the ER and the Golgi are equipped with Ca(2+)-ATPase(s).

A novel primary Ca(2+)-transport system from Saccharomyces cerevisiae

A novel primary Ca(2+)-transport system in membranes from Saccharomyces cerevisiae is described. Ca2+ transport is strictly dependent on the presence of ATP; other nucleotides like GTP, UTP and CTP do not efficiently (< 10% of the rate of ATP) drive uptake. Transport is inhibited by sodium vanadate with an IC50 of 130 microM, but is insensitive to carbonylcyanide p-trifluoromethoxy-phenylhydrazone, valinomycin, gramicidin or calmodulin. Ca2+ accumulates in a free form and can be readily released by the Ca2+ ionophore A-23187 or by osmotic shock. The apparent Km values of transport activity for free Ca2+ was determined to be 0.11 microM and 5 microM for Mg.ATP, respectively. Taken together the results indicate that the Ca2+ transport described here does not belong to the plasma-membrane-type Ca(2+)-ATPase family but rather to the family of endomembrane-type ATPases. Cell-fractionation studies of crude membranes on sucrose gradient centrifugation have shown that the Ca(2+)-transport activity separates from marker enzymes for endoplasmic reticulum, vacuole, or plasma membrane and migrates with GDPase activity, a marker for the yeast Golgi complex.

Change in transport activities of vacuoles of the yeast Yarrowia lipolytica during its growth on glucose

Vacuoles were isolated from Yarrowia lipolytica yeast cells taken at various growth phases under carbon or nitrogen limitation. Vacuoles from the cells at the logarithmic growth phase showed a high activity of vacuolar H(+)-ATPase (0.9-1.1 U/mg protein) and efficiently generated chemical proton gradient and membrane potential across the tonoplast. Ca(2+)- and citrate transport were found to be maximal at this growth phase. At growth retardation and then in the stationary phase all the parameters studied decreased irrespective of the method of growth limitation. The citrate-transporting activity of vacuoles completely disappeared at growth retardation, also irrespective of the limitation method and irrespective of whether yeast cells overproduced citrate in the culture medium. The citrate-transporting system of Y. lipolytica vacuolar membrane is concluded not to be involved in citrate efflux and this efflux is probably performed by the plasmalemma transport system.

Mercaptoethanol and dithiothreitol decrease the difference of electrochemical proton potentials across the yeast plasma and vacuolar membranes and activate their H(+)-ATPases

Mercaptoethanol and dithiothreitol (DTT) inhibited the acidification of external medium by Saccharomyces carlsbergensis cells and protoplasts during glucose oxidation. The inhibition was also observed when cells were incubated with mercaptoethanol or when mercaptoethanol and DTT were used to prepare protoplasts. Experiments with S. carlsbergensis plasma membrane vesicles and vacuoles showed these thiol reagents to inhibit ATP-dependent generation of delta pH and Em across plasma membrane vesicles and vacuoles but to activate their H(+)-ATPases. Mercaptoethanol and DTT are suggested to de-energize plasmalemma as well as tonoplast by increasing their H(+)-permeability and to disturb the cell ion homeostasis.

Purification and some properties of membrane-bound and soluble pyrophosphatases of yeast vacuoles

The membrane-bound and soluble pyrophosphatase (PPase) activities of Saccharomyces carlsbergensis vacuoles are determined by the functioning of special enzymes and are not due to non-specific PPi hydrolysis by other vacuolar phosphohydrolases. The molecular mass of the membrane-bound PPase is apparently 120,000 and its molecule consists of three subunits with Mr = 41,000. Soluble PPase has a molecular mass of about 82,000 and includes three subunits with Mr = 28,000. Both enzymes are glycoproteins. The vacuolar membrane-bound PPase is a proton pump.

The fungal vacuole: composition, function, and biogenesis

The fungal vacuole is an extremely complex organelle that is involved in a wide variety of functions. The vacuole not only carries out degradative processes, the role most often ascribed to it, but also is the primary storage site for certain small molecules and biosynthetic precursors such as basic amino acids and polyphosphate, plays a role in osmoregulation, and is involved in the precise homeostatic regulation of cytosolic ion and basic amino acid concentration and intracellular pH. These many functions necessitate an intricate interaction between the vacuole and the rest of the cell; the vacuole is part of both the secretory and endocytic pathways and is also directly accessible from the cytosol. Because of the various roles and properties of the vacuole, it has been possible to isolate mutants which are defective in various vacuolar functions including the storage and uptake of metabolites, regulation of pH, sorting and processing of vacuolar proteins, and vacuole biogenesis. These mutants show a remarkable degree of genetic overlap, suggesting that these functions are not individual, discrete properties of the vacuole but, rather, are closely interrelated.

Deuterons cannot replace protons in active transport processes in yeast

Replacement of ordinary water with heavy water causes a sharp reduction of the rates of both primary hydrogen ion transport (at the plasma membrane ATPase) and secondary symports (H(+)-associated transports of sugars and amino acids) in several species of yeast. At the same time, the hydrolytic activity of the ATPase is affected only very little. Likewise, the membrane potential, the delta pH and, correspondingly, the accumulation ratios of the various symported solutes are altered much less. This serves as evidence that H+ or H3O+ ions are direct participants in the various active transports of nutrients in yeast.

Synthesis and secretion of bacterial alpha-amylase by the yeast Saccharomyces cerevisiae

Alpha-amylase from Bacillus amyloliquefaciens, synthesized in yeast Saccharomyces cerevisiae without substitution of the signal sequence, is efficiently secreted from yeast cells: 60-70% of the overall amount of the enzyme is found in the culture fluid. In contrast to many yeast secretory proteins, which accumulate in the periplasmic space and in the cell wall, intracellular alpha-amylase is localized mainly in the cytoplasm. Obviously, transfer across the cell wall is not a rate-limiting step in alpha-amylase export from the cell. The glycosylated forms of proteins are predominantly found both inside the cell and in the culture medium.

Cation-stimulated ATPase activity in purified plasma membranes from tobacco hornworm midgut

Purified goblet cell apical membranes from Manduca sexta larval midgut exhibit a specific ATPase activity approx. 20-fold higher than that in the 100 000 X g pellet of a midgut homogenate. The already substantial ATPase activity in this plasma membrane segment is doubled in the presence of 20-50 mM KCl. At ATP concentrations ranging from 0.1 to 3.0 mM, the presence of 20 mM KCl leads to a 10-fold increase in the enzyme's affinity for ATP. ATPase activity is greatest at a pH of approx. 8. In addition to ATP, GTP serves as a substrate, but CTP, ADP, AMP and p-nitrophenyl phosphate do not. Either Mg2+ or Mn2+ is required for activity and cannot be replaced by Ca2+ or Zn2+. The ATPase activity of goblet cell apical membranes is inhibited by neither the typical (Na+ + K+)-ATPase inhibitors, ouabain and orthovanadate, nor by the typical mitochondrial F1F0-ATPase inhibitors, azide and oligomycin. Although 1.5 microM DCCD is ineffective, 150 microM DCCD leads to total inhibition of ATPase activity. The ATPase activity of goblet cell apical membranes is stimulated not only by K+, but also, in order of decreasing effectiveness, by Rb+, Li+, Na+ and even Mg2+. Replacement of Cl- by Br-, F- and HCO3- has less influence than variation of the cations. However, replacement of Cl- by NO3- inhibits strongly this ATPase activity. The ATPase activity described above is characteristic of the alkali metal ion pump containing apical membranes of goblet cells and is not enhanced to a similar degree in other purified midgut epithelial cell plasma membrane segments. Its localization, its broad cation specificity and its insensitivity to ouabain all mimic properties of active ion transport by the lepidopteran midgut and suggest this ATPase as a possible key component of the lepidopteran electrogenic alkali metal ion pump.

H+/ion antiport as the principal mechanism of transport systems in the vacuolar membrane of the yeast Saccharomyces carlsbergensis

The secondary transport systems of the yeast vacuolar membrane have been investigated by the method of radioactive isotopes [( 14C]arginine); activation of H+-ATPase by cations (Cat+), when the enzyme is under H+ control and measurement of changes in the proton gradient (delta pH) and membrane potential (Em) due to the supposed substrates of the transporters. The main mechanism of cation transport across the yeast tonoplast is probably H+/Cat+ antiport. The apparent Km of antiporters for Ca2+, Mg2+, Mn2+, Zn2+ and Pi are 0.06, 0.3, 0.8, 0.055-0.17 and 1.5 mM, respectively.

What family of ATPases does the vacuolar H+-ATPase belong to?

Polyacrylamide gel electrophoresis (PAGE) of partially purified ATPase from vacuoles of Saccharomyces carlsbergensis under non-dissociating conditions revealed 3 bands with ATPase activity. Further PAGE in dissociating conditions showed the similarity in composition of these 3 ATPase preparations. They were assumed to contain the same vacuolar ATPase exhibiting, however, different electrophoretic mobility due to the formation of enzyme complexes with different proteins and phospholipids. The ATPase preparation with the highest electrophoretic mobility contained 6 subunits of 75, 62, 16, 14, 12 and 9 kDa. Inhibitors of vacuolar ATPase [14C]DCCD and [14C]NEM bound to a 9 kDa polypeptide, while [14C]DES associated with a polypeptide of 75 kDa. A partially purified preparation of the vacuolar ATPase was not phosphorylated by [gamma-32P]ATP under conditions when plasma membrane ATPase formed a phosphorylated intermediate. Our results show that vacuolar H+-ATPase consists of several polypeptides, does not form the phosphorylated intermediate, and evidently represents a new type of H+-ATPase of yeast.